400 series stainless steels has an 11 percent chromium and 1 percent manganese increase, above the 300 series group. The 400 series is susceptible to rust and corrosion under some conditions. Heat treating will harden the 400 series. Fast Lane has experience with all the different 400 series steels. One of our specialty is hydraulic system parts such as orfices poppets, spindles, spools, bodies, shuttles, pistons ect. Many of these parts require outside process after machine work like heat treat, grinding, plating, honing to match fit mating parts. We only use qualified outside houses for these processes. We have machined 400 series on our 5 axis mill down to our 12mm Swiss machine.